In the production of fibers which undergo color change with temperature, application of a liquid crystal ink has been proposed in Japanese Patent Publication No. 2532/76. This technique comprises coating a liquid crystal ink on one or both sides of a sheet base of a deep color, e.g., black or deep blue, and cutting the coated sheet to form flat yarns or twisting the flat yarn around a core yarn to form twisted yarn. Therefore, the product is a sheet rather a fiber, as having a special shape different from general fibers. The freedom of forms and properties are so limited that requirements on various shapes according to purposes cannot be satisfied. Use of a liquid crystal per se extremely reduces moisture resistance making it impossible to wash the product. Further, this technique involves additional disadvantages in that colors of the product are limited only to deep ones; color change temperatures cannot arbitrarily be selected; and a high cost is entailed. In some detail, although the sheet product having a thermochromic coating even on both the upper and lower surfaces thereof, both of the two cut edges thereof are not coated with a thermochromic layer. If in cutting the thermochromic layer-coated sheet in narrow ribbons, the proportion of the surface coated with the thermochromic layer is reduced to 1/2 or even less, resulting in an extremely deteriorated thermochromic effect. These disadvantages have permitted of no practical use. Accordingly, it has been keenly demanded to develop fibers which can change in a wide variety of colors at optional temperatures.